Ex-vivo evaluation of the intestinal uptake of calcium contained in water or in vitro digest of Grana Padano cheese

Dietary calcium (Ca) introduced in the Italian population is lower than the recommended daily intake and it is mainly linked to the consumption of dairy products, although several studies consider mineral waters an important Ca source. The aim of this work was to compare ex-vivo the intestinal absorption of calcium provided by an in vitro digest of Grana Padano cheese or a CaCO3 solution. The intestinal bioavailability of Ca was determined ex-vivo with the Ussing Chambers (UC) technique, which uses segments of rat intestine, kept alive and viable. UC consisted of a thermostated assembly (37 °C) which housed six cells, equipped with an O2 infusion system. Each cell consisted of two semi-cells that represent the two sides of the intestinal barrier: the mucosal, internal to the small intestine, and the serosal. To keep intestinal tissue alive and vital, a specific physiological solution was placed in both cells. The small intestine segments were taken from adult rats and fixed on the half-cell within 1 h from collection. Grana Padano PDO cheese ripened 10 months was in vitro digested using the INFOGEST static protocol. Oral phase: 5 g of Grana Padano ground in 5 mL of simulated salivary liquid (SSF) at pH 7.0 for 2 minutes. Gastric phase: The derived bolus was mixed with 10 mL of simulated gastric juice (SGF) and pepsin (1000 U mL-1 of SGF), adjusted to pH 3.0 with HCl and incubated at 37 °C for 2 h. Intestinal phase: addition of 20 mL of simulated duodenal juice (SDF) and bile salts (10 mM/L) and trypsin (100 U mL-1 SDF), chymotrypsin (50 U mL-1 SDF), lipase (2000 U mL-1 SDF) and co-lipase (lipase/colipase molar ratio: 1/2). The intestinal digestion was carried out at 37 °C and pH 7.0 for 2 h. The Ca content of the digested Grana Padano cheese was 7935 mg/L, while the CaCO3 solution had a concentration of 54.1 mg/L of Ca. Results showed that the intestinal absorption of Ca contained in cheese digest was greater (74.8% vs 44.3%, p<0.0001) than that obtained for the CaCO3 solution. This finding is likely due to the presence of casein phosphopeptides, which promote intestinal Ca absorption, highlighting the importance of Grana Padano as dietary Ca source. Future in vivo studies will be carried out to evaluate the effect of Grana Padano cheese on bone mineral density.